1. Field of the Invention
The present invention relates to a L-type zeolite, a catalyst for the production of aromatic hydrocarbons and a process for producing aromatic hydrocarbons by the use thereof and more particularly, to a L-type zeolite with a platinum component and a halogen component supported thereon, a catalyst comprising the L-type zeolite suitable for the aromatization reaction and a process for efficiently producing aromatic hydrocarbons from non-aromatic hydrocarbon such as paraffin series hydrocarbon by using said catalyst.
2. Description of the Related Art
Conventionally platinum.alumina series catalysts have been put to use as the catalyst for producing aromatic hydrocarbons by aromatizing non-aromatic hydrocarbon such as aliphatic hydrocarbon and in recent years there have been proposed the methods of using catalysts which contain L-type zeolite and platinum supported thereon, having an improved conversion efficiency (Japanese patent publication No. 57408/1983 and Japanese patent application LAID-OPEN Nos. 223614/1983 and 80333/1984).
However, all of platinum-supporting L-type zeolite catalysts used in these methods have not been found satisfactory because they have a low selectivity of aromatic hydrocarbons and a short catalyst lifetime. Meanwhile, a platinum-supporting L-type zeolite catalyst to which an alkaline earth metal (Ba, Sr, Ca) is introduced has been proposed as the improvement of said defects (Japanese patent application LAID-OPEN No. 133835/1983), but the follow-up study of the present inventors has resulted in a finding that this catalyst also is of no practical use as its selectivity of aromatic hydrocarbons and a catalyst lifetime are not sufficiently improved, along with a low catalysis stability.
There have been further proposed (1) a catalyst improved in catalytic activity and a catalyst lifetime by subjecting L-type zeolite with a metal or metals of Group VIII of the Periodic Table supported thereon to the oxychlorination treatment (Japanese patent application LAID-OPEN No. 168539/1985), (2) a catalyst whereon platinum is uniformly dispersed and supported, treated with a solution consisting of platinum solution and non-platinum metal salt (Japanese patent application LAID-OPEN No. 138539/1986), (3) a catalyst wherein platinum is supported on L-type zeolite treated with a halogen-containing compound (Japanese patent application LAID-OPEN No. 57653/1987), (4) a catalyst containing L-type zeolite with platinum supported thereon which is treated with a halogen-containing compound (Japanese patent application LAID-OPEN No. 91334/1988) and the like.
However, the catalysts mentioned in (1) are extremely poor in economical efficiency because of expensive equipment required for their production processes to carry out the oxychlorination treatment at high temperatures, while the catalysts of (2) do not show sufficient catalytic activity. Relative to catalyst of (3) and (4), though their catalytic activity is improved, they are still short of a sufficiently long term of a catalyst lifetime and require equipment of special type to deal with halogen components. Furthermore, it is desirable not to use these catalysts in points of the environmental protection as the halogen-containing compound to be used in their production processes is Flon gases (fluoroalkanes, chlorofluoroalkanes) which are controversial for their adverse influences on environment.
As mentioned above, the problems of the conventional catalysts lie in their production processes, catalytic activity, catalyst lifetime and the like, but a satisfactorily useful catalyst has not as yet been proposed.
Thus the present inventors have made intensive studies with a view to improving the defects of the conventional catalysts and developing a catalyst for the production of aromatic hydrocarbon which can be obtained by simple production processes without the need of special equipment, exhibiting an improved activity and having a longer term of catalyst lifetime. As the result, it has been found that above-mentioned object can be achieved by a catalyst comprising L-type zeolite and both a platinum component and a halogen component supported thereon. The present invention has been accomplished on the basis of this finding.